diff --git a/tests/test_bump.py b/tests/test_bump.py
index 2da1cc7..703491f 100644
--- a/tests/test_bump.py
+++ b/tests/test_bump.py
@@ -9,6 +9,8 @@ from __future__ import annotations
 
 import base64
 
+import pytest
+
 
 from image_tools.bump import Dependent, bump_all, load_dependents, open_or_update_pr, rewrite_pin
 
@@ -137,6 +139,72 @@ def test_the_dependents_are_listed_in_the_repo(tmp_path):
     ]
 
 
+@pytest.mark.parametrize("bad", ["", "base-os", "netork/base-os:1"])
+def test_an_odd_new_reference_is_refused(bad):
+    with pytest.raises(ValueError):
+        rewrite_pin("FROM x\n", "netork/base-os", bad)
+
+
+def test_a_repo_without_the_file_yet_is_skipped():
+    """The service repos start empty; a missing file is no pin to move, not a crash."""
+
+    class Empty(FakeGitea):
+        def __call__(self, method, path, body=None):
+            if method == "GET" and "/contents/" in path:
+                self.calls.append((method, path))
+                raise FileNotFoundError(path)
+            return super().__call__(method, path, body)
+
+    api = Empty({})
+
+    assert open_or_update_pr(api, DEP, "netork/base-os", NEW, "13-20261020.1", "r") is None
+    assert not [c for c in api.calls if c[0] in ("PUT", "POST")]
+
+
+def test_a_dependent_without_a_workflow_gets_the_pr_only():
+    """engine and satellite have no nightly run; their pull request is the trigger."""
+    from image_tools.bump import dispatch
+
+    calls = []
+    dispatch(lambda *a: calls.append(a), Dependent("NetOrk/netork", ("x",), ""), {"base_ref": NEW})
+
+    assert calls == []
+
+
+def test_a_compose_pin_with_the_registry_variable_moves():
+    """netork's compose files name the registry as ${REGISTRY_HOST:-registry.netork.io}
+    (tests/test_compose_image_names.py there); the variable stays, the pin moves."""
+    old = (
+        "${REGISTRY_HOST:-registry.netork.io}/netork/apt-cacher-ng:3.7.5-1-13-20261020.1-2026102017@sha256:"
+        + "a" * 64
+    )
+    new = (
+        "registry.netork.io/netork/apt-cacher-ng:3.7.5-1-13-20261021.1-2026102103@sha256:"
+        + "b" * 64
+    )
+    text = f"  apt-cacher-ng:\n    image: {old}\n"
+
+    moved = rewrite_pin(text, "netork/apt-cacher-ng", new)
+
+    assert moved == (
+        "  apt-cacher-ng:\n    image: ${REGISTRY_HOST:-registry.netork.io}/netork/apt-cacher-ng:"
+        "3.7.5-1-13-20261021.1-2026102103@sha256:" + "b" * 64 + "\n"
+    )
+
+
+def test_a_repo_the_bot_may_not_see_is_an_error_not_a_skip():
+    """Gitea answers 404 for the repo and its files alike when the token's account
+    has no access; on 2026-10-22 that read as "no pin to move" everywhere."""
+
+    class Invisible(FakeGitea):
+        def __call__(self, method, path, body=None):
+            self.calls.append((method, path))
+            raise FileNotFoundError(path)
+
+    with pytest.raises(PermissionError, match="NetOrk/"):
+        open_or_update_pr(Invisible({}), DEP, "netork/base-os", NEW, "13-20261020.1", "r")
+
+
 class TestEveryDependent:
     """2026-10-22: netork's dependents entry named ui-nightly.yml, which does not
     exist yet; the dispatch's 404 ended the run with a traceback after the last